Field of the Invention
The invention relates to a method for electrically conductively connecting a contact piece on the basis of copper to an electrical conductor consisting of a plurality of individual wires of aluminum, as well as a corresponding arrangement.
Description of Prior Art
The contact piece on the basis of copper consists either of copper or of a copper alloy. Additionally, it may have on its outer surface a layer of, for example, tin, zinc or nickel which are for example, precipitated galvanically. In the following, the contact piece is referred to only as “contact piece” without material identification. The individual wires of the conductor are either of aluminum or an aluminum alloy. In the following, only the material “aluminum” is taken into consideration.
Conductors of aluminum are increasingly used especially as replacement for copper conductors for reasons of weight and cost. Principal fields of use of such conductors are, for example, automobile and airplane technology. The lower electrical conductivity of the aluminum as compared to copper does not play a role for most applications. However, problems occur when placing contact parts on the conductors because aluminum conductors are surrounded by an electrically very poorly conducting oxide layer. This deficiency becomes apparent in the case of conductors which are composed of a plurality of individual wires, also called stranded conductors, each of which is surrounded by an oxide layer which cannot be avoided without special treatment. This problem has been known for a long time and is described in numerous documents, wherein the following four references shall be mentioned.
DE 102 23 397 B4 discloses a method by means of which a contact element is electrically mounted on a stranded conductor of aluminum wires. For this purpose, a metal sleeve which is covered on the inner side with tin is pushed onto the end of the stranded conductor. The individual wires are then galvanized or welded at their end faces and with the sleeve by means of ultrasound or protective gas welding. The oxide layers which surround the individual layers are to be broken open in this process. This results in a cover-like tinning or welding at the end of the stranded conductor. Finally, the contact element is pushed on and pressed together with the end of the stranded conductor. The cover-like tinning or welding is not included in the pressing procedure.
DE 103 46 160 B3 describes a method for contacting an aluminum conductor constructed as a stranded conductor in which a contact clamp, which is coated with tin on the inner side and composed of copper, is pushed onto the end of a stranded conductor consisting of aluminum. The tubular contact clamp is coated with tin at the end face of the aluminum conductor by means of ultrasound tinning together with the same, or is welded metal against metal by means of a known welding method.
In the method according to DE 103 57 048 A1, a supply of contacting agent is applied to the end of an existing stranded conductor and is heated at least up to the range of its melting temperature. In so doing, through the contacting agent for forming an electrical contact, a material connection is to be obtained between the stranded conductor and a cup-shaped contact element which is simultaneously or subsequently pushed onto the stranded conductor. For applying the contacting agent, the stranded conductor can be dipped into a tin bath, thereby a portion of the stranded conductor can be severed or cut for forming a fresh cutting or severing surface in the tin bath. The contact element is pressed around the stranded conductor with decreasing effect of the tension.
DE 10 2011 018 353 A1 describes a method for connecting a contact part with a stranded conductor consisting of aluminum. A support sleeve is mounted on the stranded conductor at its end and is pressed together with the same. Subsequently, a rotationally symmetrical contact part is welded to the end face of the stranded conductor, for example, by means of rotational friction welding. In this method, an inter-metal is formed between the contact part and the stranded conductor.